1. Field of the Invention
The present invention relates generally to network-attached data storage, and more particularly, to client access of network-attached data storage in an Internet Protocol (IP) network.
2. Description of Related Art
Local disk drives are typically coupled to a host computer over a parallel interface, such as a Small Computer System Interface (SCSI). A SCSI port provides a data bandwidth of up to 80 megabytes per second, and multiple disk drives can be attached to a single SCSI port. A SCSI port can also be used to couple a storage system to a host. The storage system, for example, may use a redundant array of inexpensive disks (RAID).
Various SCSI standards are published by the International Committee for Information Technology (NCITS), Information Technology Industry Council, 1250 Eye Street NW, Suite 200, Washington, D.C. 20005. For example, there is a standard set of SCSI-3 block commands for transferring data in blocks from random-access devices such as hard disks. The full set of block commands are set out in the standard NCITS.306-1998, and a reduced set of block commands are set out in the standard NCITS.330-2000.
Storage systems have also been developed that provide continuous storage availability over network-attached storage. This has been done effectively by clustering front-end processors to back-end RAID storage, and having the storage addressable by both file and block applications. Block applications, for example, may send SCSI-type block commands to the network-attached storage. In many situations, it is desired to send SCSI-type block commands over an Internet Protocol (IP) network, such as a 10-base-T IP network, a Fibre-Channel IP network, or the Internet. For example, an IP-network solution may have a lower infrastructure cost for a given level of performance, or it may be desired to add reliable backup storage to an existing IP network. Unfortunately, for block applications, the IP network has been a bottleneck in the data path.
One proposed way of addressing the problem of providing block services over an IP network is to traverse the IP stack and attempt to convert file formats to block formats, and then block formats back to file formats, in order to attach storage directly to the IP network. However, this has been seen as removing the simplicity of the network-attached solution. Therefore, IT organizations have been advised to examine network-attached solutions for file services and channel-attached solutions (e.g., Ultra SCSI, Fibre Channel) for block services, while understanding the benefits and limitations of each storage architecture. See Sean Derrington, “NAS and SAN Storage: Separate but Equal?—Part 2,” File 838, Server Infrastructure Strategies, Meta Group Inc., 208 Harbor Drive, Stamford, Conn. 06912-0061, Jun. 12, 2000.